Ventilation of building's occupied by humans is required. Such ventilation is required to provide fresh oxygen to the occupants of the building and to remove stale air with high concentrations of CO2 for health and comfort reasons. Modern construction and building codes have imposed certain requirements on building ventilation systems. In particular modern construction focuses on heavily insulated and air tight buildings to reduce overall energy consumption. Making the building substantially airtight limits the amount of energy loss through drafts and the like.
On the other hand, modern building codes require a sufficient turnover of air within a dwelling in order to provide sufficient fresh air and oxygen for the occupants to be healthy and comfortable. Certain technology and equipment have been developed to meet with these competing demands. In particular, specialized ventilation units have been developed to provide a source of fresh air while at the same time limiting the amount of energy lost through the exhaust airstream.
Such devices are called heat recovery or energy recovery ventilation units and may be referred to in northern climates as HRVs. In southern climates they are referred to as energy recovery ventilation devices or ERVs. Essentially, the only difference between these two units is that an HRV captures heat energy from the exhaust airstream, whereas an ERV reduces a cooling load imposed by the fresh air stream.
Typically, these devices comprise a body containing an air to air heat exchanger. The exhaust airstream is passed through one side of the heat exchanger while the fresh air stream is passed through the other side of the heat exchanger. In this way the airstreams are allowed to exchange energy by means of a counter current heat exchange, without the airstreams being in direct contact or being allowed to mix with one another. Thus the quality of the fresh air is preserved.
Again typically, HRV and ERV devices include small fans to drive the air through the heat exchanger. Ideally the flow of fresh air into the building should be equally matched by the flow of stale air being exhausted out of the building. Although the fans can be calibrated in a factory setting to a predetermined flow rate, site-specific installation parameters can affect the aerodynamic head for the inflow and outflow lines and thus volumetric performance of the fans.
As a result there is understood to be a need to balance the airflow streams manually for each ERV/HRV installation for example through the use of manually adjustable dampers that restrict the airflow through the conduits leading to the fans. This balancing is accomplished by means of a skilled technician using small airflow measurement devices called pitot tubes, which may be temporarily installed on the respective airstreams to measure and calibrate the incoming and outgoing airflows. Then the airflow through an individual fan can be site adjusted by a technician by adjusting dampers until the visual inspection of the pitot tubes reveals a balanced airflow across the ERV/HRV for that specific location at that specific time.
Unfortunately, this airflow balancing adjustment requires considerable time from the technician and there is no easy way for a building occupant to be able to tell if it is been done correctly, or indeed, if at all. In some cases this balancing step may be skipped by the installer to save money. In other cases changes to the airflow system or in air pressure can affect the balancing and so what might have been balanced at one point can get out of balance. Further there is a tendency for the fan characteristics to change over time, due to changes in the lubrication and wear on the mechanical parts, or even an accidental change to the baffle position during routine maintenance or the like of the unit. In most cases the units will include removable filters which require periodic cleaning meaning that the unit is opened and the sensitive elements, such as the baffles, are exposed. None of these potential unbalancing changes can be accurately detected without a return of the technician and a recalibration of the system by means of the pitot tube measurements. Therefore there is a need for an improved way of balancing the air flows through ERVs and HRVs.
Examples exist in the prior art that attempt to improve airflow balancing in these types of ventilation units. For example, U.S. Pat. No. 7,458,228, is directed to some of these issues. However in this device a single motor is used to drive two fans. Adjustment of the airflow is accomplished by means of movable dampers which restrict the air flow by closing one or the other the air flow pathway to a certain extent. This patent teaches that balancing is achieved by determining the first static pressure difference in the fresh air path by using first and second static pressure sampling locations and then determining a second static pressure difference in the exhaust air path using third and fourth static pressure sampling locations comparing the predetermined exhaust air flow value corresponding to the first static pressure difference with a predetermined exhaust air flow value corresponding to that second static pressure difference to determine if a predetermined fresh air and exhaust air flow values are at least substantially equal. Again, this invention requires the use and installation of pitot tubes, and manual adjustment of fan dampers. Further, this system cannot adjust to changes in the airflows over time, without some intervention of a skilled technician.
Other examples of prior disclosures which address the issue of balancing air flows include U.S. Pat. Nos. 6,289,974; 7,007,740; 7,458,228; 7,656,942; 7,795,827; and U.S. Publication Application Nos., 2001/0030036A1; and 2002/0017107 A17. While interesting, none of these prior devices overcome the issue of requiring a manual measurement and then manual adjustment of for example movable dampers for the airflow to be balanced across the ventilation units. Thus, none of these prior disclosures overcome the issue of requiring a re-attendance of a skilled technician to deal with any changes that might occur to the airflows over time.